Hi Stu,
I did just that. Thanks. I called Warren Pandy at Catalina this am. For the benefit of anyone else considering this particular repair on the 310, he said that due to the different ages of the Catalina 310, and changes that may have been made during the course of its production, some boats may have that particular stanchion base through bolted and some may be screwed into deck plates. His good advice to me was to take a Phillips screw driver and try to back out one of the screws on the base plate of the stanchion. If it turns readily, and keeps turning, it is likely in a deck plate and I have a beer. If it doesn't then it was probably through bolted. If that is the case, he said I could simply cut an access hole with a hole saw etc. in the back of the cabinet itself to access the bolts and then install an access hatch for future rebedding f I wish.
I probably should have thought of that before asking the wisdom of this forum. However, I was hoping to hear that someone had done all their stanchions and would tell me, point by point, how they did it for each of the stanchions. Anyway, I will post the results of my stanchion and chainplate rebedding work on the forum to the extent anyone might be interested. I will take photos.